The invention relates to a light fitting unit for illuminated signs having a low current input, and a housing for mounting a plurality of light emitting diodes.
Illuminated signs with in the meaning of this patent application are in particular the signs commonly used in the USA to indicate exits. These signs generally comprise a flat, block-shaped housing having two opposite main surfaces. At least one of the two main surfaces has apertures forming the letters to be displayed and other symbols where necessary. In the case in question, the apertures form the word EXIT. The apertures are generally backed with a filter sheet to ensure an even and diffuse light radiation of the illuminated sign.
For illumination, light sources are provided inside the housing. According to the prior art, two or more bulbs are disposed behind the surface provided with apertures. A drawback of the use of bulbs is however that the letters formed by the apertures are only illuminated very unevenly. This unevenness is detrimental to legibility at long distances. To improve the legibility of the sign, bulbs with a high luminous power must be used. This leads to a high power consumption by the illuminated sign. A further drawback is that bulbs have a very limited life, hence impairing the reliability of the illuminated sign.
In the prior art, the substitution of bulbs in the above illuminated signs by light fitting units having a plurality of LEDs is also known. A light fitting unit of this type comprises a rod-like housing body in which a plurality of LEDs are arranged in a line along a lateral surface. These rod-like light fitting units are attached to two opposite lateral surfaces of the housing such that the LEDs radiate mainly parallel to the main surfaces of the illuminated sign. The sign is therefore mainly illuminated by diffusely reflected light. A drawback of these known light fitting units is however that the provision of LEDs on the lateral surfaces means that the letters in the illuminated sign are only illuminated very unevenly, with the brightness decreasing towards the center of the sign. Additional diffusely reflecting parts are therefore necessary for even illumination. A further drawback of these light fitting units is that letters or symbols directly above them are only insufficiently illuminated on account of their lateral attachment. Furthermore, the lateral arrangement has the drawback that bulbs cannot be replaced later on by the known light fitting units.